The present invention relates to vacuum-type circuit interrupters such as are used in electrical power transmission and distribution, and switchgear assemblies. In a vacuum-type interrupter a pair of current carrying contacts are moved apart to effect arcing and then circuit interruption.
The use of magnetic forces to act upon the arc current between the contacts is well known in the art. It has been the general practice to design the contact structure such that a magnetic field is generated which interacts with the arc current to drive the arc current circumferentially around the contact surface. More recent developments have indicated that a magnetic field which is directed along the arc current axial path, and which axial field is parallel to the arc current, is advantageous in that it produces a diffuse arc. The more diffuse the arc, the less the erosion of contact material upon successive operations, and in general, the greater the capability of the device to handle higher power interruptions reliably.
The axial magnetic field in such devices was originally generated externally of the sealed vacuum envelope. Recent work has focused on designing a contact structure which incorporates axial field generating means as part of the contact structure, or closely associated with the contact. A recent example of such structures is U.S. Pat. No. 4,117,288, issued Sept. 26, 1978 and owned by the assignee of this invention.
A variety of other axial field contact interrupter devices are known in the art, but are relatively complicated to manufacture or offer limited current carrying capability.
It is important that any vacuum interrupter which incorporates an axial field means, as part of the contact structure, be as structurally simple as possible to improve reliability and lower manufacturing cost. The contacts must be rugged to withstand the closing action in which the contacts are slammed together, and to permit repetitive opening and closing.
In an axial field contact in which the current is passed through the field generating conductor the structure should be such as to minimize losses while carrying significant currents.